I would use the primer. Quick drying, porous, underlying (old) concrete will wick the water out of your leveling mix, which is worse for it then it is for a comcrete pour.
In Las Vegas, when they mistakenly sent winter mix concrete to pour 4 house post-tension slabs, and the weather was unusually warm and windy as heck, we had 3 develop major cracking on the house slab and all 4 bad cracking on the garage slab. The thick house slabs also shrank considerable, leaving lots of low spots. And because it dried so fast, they werent able to get a good smooth screed/steel float, so there were high spots too that had to be ground.
They tried twice to use a leveler w out bonding primer and got cracking and flaking of it so bad it had to be removed.
Waited for walls and 2nd floor decks to go on, used primer and no problems.
As the houses were pre-sold, it was a mess and took an extrodinary effort to make it acceptable to the buyers, as it all had to be disclosed. All 4 garages got free optional upgrades to the color flake/epoxy garage coating.
In April, it can still get down into freezing over night, hence the winter mix.
EDIT oops, I thought you were still talking about the leveler.
No, dont use primer w the thinset, if you're wet setting the tile into it. Back butter the tiles really well w the flat side of your trowel, then rake it w the 1/4in notch (correct?)
