im guessing you want 1.5's so you dont have to high of lift on stock springs?

Your best bet is to find ls6 springs used on tech or somewhere and slap those on since they hold .550 lift I believe(its 2-3 different color ones for different lifts)

but putting 1.5's on to keep the lift down so the stock springs work is cancelling out even doing a cam

if thats the case, get a custom grind cam with low lift and keep the stock rockers:-P

i wanted to put 1.8's on mine but my springs only hold .550 and im at .531 now