Is this a logical reason to change a baby’s name?

Have you asked your family why they don’t use the baby’s name? If they aren’t sure how to pronounce it it then help them. If it’s a difficult pronunciation for a non Spanish speaker then accept some reasonable variation in pronunciation so long as it’s still the name. Say her name a lot in the presence of everyone, make it really familiar. It’s her name and everyone will get used to it.

You haven't mentioned what your husband says about your flipflopping on your child's given name.
When you stated "our first names are a core part of our identity"..you're corrent..hence names are deliberated over and discussed before being registered...not just given off the cuff.
Why are you now wanting to change?
It's the child's name, it doesn't belong to anyone else.

The child's identity and heritage are half Spanish...don't now try to erase that fact.. just because some people you know..(you don't actually know, you're just assuming..) are too lazy to pronounce it.

I think it depends on the name. Cruz for example, I wouldn’t be sure how to say (I think pronounced “Cruth” in Spain). Lucia (maybe more Italian) I’d say looch-ia. But surely you will let people know how to say eg nursery. Can you tell us the name or a similar one so we can work out which category it falls into?

I think if you're raising a child in the UK and want to give a name from another culture you have to consider pronunciation. British people are notoriously bad at accents and pronunciation in other languages so it's setting them up to fail. Would you tell us the name?

Could you save the time, effort, complication (and she will have to declare all names since birth on DBS and any foreign visa applications for the rest of her life and explain her birth certificate not matching her changed name on the deed poll forevermore) and just give her a pronounceable nickname like Bea or Allie instead?

Parents who choose names that are difficult to pronounce are usually confident in their choice and don’t mind correcting people. But if you’re finding it hard and already feeling unsure, that may be something your child picks up on too, and they may end up disliking the name. In my opinion, I’d just change it.

Is it Alejandra or Luz, OP? I always struggle with those ones. I’m certain there’s more that I’m not thinking of.

I think change it. Or she'll spend her whole life giving every new acquaintance a lesson on how to pronounce her name. Either that, or start introducing her by a shortened, easier version, English sounding eg "bea". That's what she might have to start doing anyway when shes older.

Is it something like Beatriz where you say it as Beh-ah-TREEZ and they think 'It's something like Beatrice but I'll get it all wrong so I'll just say little girl'?

Or is it something like Iratxe - if you'd never seen it before you might think 'bloody hell, how do you say that?' . Apologies to any Iratxe reading and it's a Basque name not Spanish.

First one, persevere with it and put up with the odd 'Beatrice'
Second, ask close friends/family why they're not actually using it.

Can you tell us the name?

if it’s a really tough one to pronounce then just teaching your family isn’t going to help her long term. She may be happy to correct people of course but if people are actively avoiding it then it’s not great. Will it be a problem at school for example.

is there a shortening they could call her? I know someone with a dd with a hard to pronounce Portuguese name - it’s almost impossible for an English person to make the required sound or even recognise the letter makes that sound. They gave her a nickname for school but still use her full name themselves and with family etc

What's her name?

Teach people the name? Is it hard to pronounce in English?

Our children have Scandinavian names and they accept the British way of saying out and around.

I wouldn't change baby's name.

I’d change it.

Hard to comment without knowing the name OP! Does she have a middle name she might want to use when older- IF she finds it an issue?

Is it a name that looks unpronounceable to a non-Spaniard?

Surely in a few years she’ll be able to say her name herself so it won’t be a problem then? What’s the name?

I wouldn’t change it at this point. What’s the name? Maybe work on an easy to pronounce nickname

Is it something you almost need to put on a Spanish accent to say? That will give her some interesting pronunciations over her life. I wouldn't officially change her name, and her spanish side of her family will be fine. Is there a shortening or second name you could call her day to day in England?

Maybe offer to teach them how to say it? What's the name? I wouldn't change it. Once she's old enough she'll let people know how to say it I'm sure. If you love the name keep it.