KLIA2 is the replacement of the LCCT and just opened in May (after much delay). I personally have not used it yet. Yes Air Asia uses it.

I would not in the past have done such a connection given the propensity for AirAsia flights to be late and the slightly long transfer from the old LCCT to KLIA1. You could also hit a bad time to clear immigration at the old LCCT. One assumes that this should have improved with the new KLIA2 but with Malaysia...

However, with the KLIA Ekspres Train it does make the transfer easy and a very quick few mins. However, perusing the trains times they run every 20 mins at that time of day. If you say miss the 12:15 you then have to wait for the 12:35 https://www.kliaekspres.com/klia2/ which means probably missing your TG check in. Immigration at KLIA even on a Sunday lunch should be okay but hit a line and you are done, especially with 2 or more. Perhaps, if it was just you and you don't mind the challenge?

It seems a little too tight to me factoring in AA propensity to be late, two immigration trips and the 20 min headway of the train. (Though I'd probably give it a whirl as I like such challenges).