Changing terminals Kuala Lumpur - how much time?
 

Hello everybody,

I will need to change terminals in Kuala Lumpur, arriving on a domestic Air Asia flight from Penang and departing international with Turkish Airlines.
So far, I think I got the necessary information on how to make that transfer (register for free shuttle bus or pay a small fare to take the train) from the airport's website. But still no rough guidance on how many hours I should calculate, with some buffer time for delays, checkpoints, etc.

Date and times: Monday, February 18th. Many options to fly from PEN throughout the day. Flight from KUL to Istanbul leaves at midnight.
Luggage: I will have one checked bag which I will need to collect at klia2 and re-check at KLIA.
Class: Regular/eco on Air Asia, business class with Turkish Airlines

Questions:
How many hours would you recommend to make this connection?
(I'd probably add an extra hour for possible delays on the flight from Penang to KUL.)
Does traveling in business expedite the usual steps to get to the gate? (fast track security, I guess?)
Is there any benefit in using the train to transfer between klia2 and KLIA and not the complimentary bus shuttle?

Many thanks in advance.