My advice would be to spend as much as you can – you get what you pay for.
At the budget end of the market, your options (as you have found out) are quite limited.
I would make sure that you get 15″ drivers if you are not planning on buying any subs – a decent sub will set you back around £500 for one from any brand. Buy 12″ drivers if you are getting a sub though.
Personally, I use a pair of Mackie Thump 15’s – I’ve had them since December and love them – note that these are the 2014 model actually called “Mackie Thump 15” and not the eariler version called “Mackie Thump TH-15A). The older model is much less powerful and sounds a lot worse – these have the grey grill on the front whereas the new ones have a black grill.
These will cost around £500 GBP for a pair.
Another option which gets good reviews are Alto TS115A – these will also cost around £500 GBP for a pair and receive good reviews.
Slightly upmarket, I have heard a lot of positive feedback about FBT X-Lite 15’s – These will cost around £650 a pair but apparently are worth the difference.
I would not pay any less for a pair of speakers – they will not do your music justice.
bob6397