Hmm, you haven't actually had the "engagement" you planned, you aren't looking to get married for 15 months and you have mentioned on venue how many times? Op, have you turned into a wedding bore already?
It's easy to do, if you are excited About planning it, but he's not at the planning wedding stage and you keep talking about it, not just mention once, you say repeatedly.
Do you roughly know your budgets? Can you work it out yourself? What can you afford from savings and what could you reasonably expect to save between now and then? Would your family offer any help?
Do a list of who you think should be the most important people there, then a b list of others you like to have but not vital. Price up things like flowers, photographers, cakes etc lots I wedding magazines have lists of average spend you can use as a template. None of this needs to be mentioned to your DP now.
After valentines day, show him what you've worked out, see of he agrees with budgets you've set, then start calling venues to set up viewings of that are in your budget per head.
Just picking a venue first, without having a list of numbers or an idea of your budget is a really silly way to do it.
Oh and op, some men like wedding planning and find it exciting, some find it a boring chore. If your DP is in the latter category, he will not get all excited with you no matter how much you want him too, this doesn't mean he doesn't want to get married, it just means he doesn't want to arrange a wedding. You are going to have a very stressful 15 months if you keep trying to get him excited about the planning of a wedding, and constant going on about it might spoil his actual excitement about marrying you.