How on earth is your mortgage £1500 pm when you bought in a cheap area 15 years ago? What's the rate and how much equity do you have?
That payment suggests that you've borrowed a lot extra or your interest rate is pretty awful by current standards - have you looked at improving your rate? Have you always applied for a new mortgage when your current deal runs out? If you're on the standard variable rate, that can be a rip off, so unless you have bad credit, or your income has dropped a lot, you really should make sure you are always on a deal, otherwise you could be throwing thousands of pounds a year in extra interest down the drain.
Or that you don't actually live in a cheap area, of course.
When you say you have remortgaged, was that to get a better rate, or borrow more money? What was that money spent on? If it was to pay off debt rather than to fund home improvements or start a business or similar, that suggests that you may currently have a lot of unnecessary spending, that you could cut back on if you wanted to.
Not to 'never having anything nice' levels, but just cutting back a bit, combined with getting a better mortgage rate, to free up money to buy a bigger house. And if you bought somewhere closer to work to reduce travel costs and in an area where you get more for your money, that's not necessarily a rough shithole, I'm sure it must be achievable.
Also, it sounds like the Moneysavingexpert money makeover might help you go through your finances, to work out where you might be going wrong.
www.moneysavingexpert.com/family/money-help/