For your budget, get a decent(if you want better stuff, get used) 4-channel, a decent front component set, and also a subwoofer will do, skip the rear speakers, or if you want, stick wif your stocks powered by the HU.

But if your budget is 1.5k excluding install and cabling, you could work out a pretty decent setup.

For some example:
Front components: some decent 6.5" components like the PHD CF6.1(new for RM650-700)
Amp: Not too sure about this, but set aside at least half your budget for this(though i know some guy who has an Orion XTR450 for sale at about RM800)
Subwoofer: Some MTX or Kicker that works well with about 250Wrms and sealed box, i know some dude who's selling his Type-R Alpines for about RM300 each.

IMO, for audio setups, it'll only turn out nicely if you don't rush and slowly shop for good bargains(i don't call shopping from those lelong sites as bargains though, you'll never know when you actually bought authentic or fakies)

Actually 1.5k CAN actually get a pretty decent setup. Just a matter of waiting and taking time to assemble all the parts needed, especially if you get used.