Ds had severe glue ear at that stage. Although for him this showed itself in constant ear infections (about 2-3 per month).
I can't remember how long it took to be seen by ENT and they can't do a lot of testing at that age because they won't respond when they hear as an older child would.
However they do a sort of echo bounce which can show if glue ear is present, and they also have better than GP instruments to have a good look.
Glue ear can also mean a lack of balance which could explain the not walking too (although 16 months is by no means late for that)
Ds had grommets at 20 months, and it made a huge difference to him. However it depends on how bad he is, plus unfortunately on your ENT department as to how keen they can be to intervene rather than wait.
In the meantime speak lots to him, as I'm sure you do, but make sure you are facing him. Ds taught himself to lip read, which I didn't realise until it was pointed out to me. I just thought it was a cute habit of pushing my face round to him when he wanted to talk. Speak clearly, and slowly.
He may get better as the weather warms up. Ds is much better in the summer.
I would also when you see your HV ask what the waiting list for speech therepy is like, and request to go on the waiting list. In our are the wait can be a year, so if that's the case, then putting him on now is not unreasonable. If it's 6 months or less, then I would wait until he's seen ENT because the first thing SALT will ask is if he's had a hearing test.