Just take a Slann at 1500, he is so worth it. There's no reason why you shouldn't base your 1500 list around a Slann and TG - they should still be competitive. I'd even consider no other heroes until you reach 2500. I'd go for something like:
375 Slann, BSB, Extra Dice, Knows Lore, Dispel Scroll (Life magic)
331 16 Temple Guard, Full Command, Razor Standard
250 20 Saurus, Full Command
250 20 Saurus, Full Command
60 5 Chameleon Skinks
60 5 Chameleon Skinks
160 2 Salamanders, 2 Extra Handlers
Later on I would give the Slann becalming cogitation and swap the dispel scroll for feedback scroll & bane head or for cupped hands, add some skirmisher Skinks and maybe some more chameleons, add another two salamanders or a Stegadon, maybe make the Saurus units bigger and add some Stegadons (and POSSIBLY a priest on an engine, but only if you don't expect to face many cannons). Also consider the flame banner on the Slann for an uber TG combat unit (-3AS hits with re-rolls to wound when assaulting a building), but beware dragonhelm/gem heroes holding up the unit solo. Another banner to consider on the Slann is the Standard of Discipline for the amazing +1Ld.
Character light is the way forward for LM, I truly believe. Just think each time you consider adding another hero - would his points in Saurus/salamanders do more damage? Also remember that ideally a Slann would be using up all of the PD in the magic phase and so Skink priests should only really be taken for their item holding ability (cube of darkness/a scroll) or for an EotG.