Your best bet is looking though army lists at 1.5k points then and seeing what models the people are using.
1.5k hunh?
consider getting
1-2 boxes of warriors for now
some dark lance warriors (maybe 4 or 6)
9 wyches
1 wyche succubus
2-3 more raiders
lord if you dont want to convert
maybe another ravager
more jetbikes (enough to have 1 or 2 complete squads of 5, you decide)
these are more generic suggestions than catered to developing a 1.5 list, but generally overall good if your just starting DE. You can make this into a pretty good army from that, and you shouldn't have any useless models regardless of what type of army you play (unless its a really strange one:)).