No, they are completely separate terminals.

KLIA2 is the low-cost terminal, with badly organised and more chaotic immigration lines at peak times, which seems like most of the day.

KLIA is better organised, having separate "specialist" lines for business and for elderky, disabled etc But the general line can be horribly long.

Procedures at both terminals can be surpisingly fast. But that clearly depends on the the density of arriving flights. Dont bank on it!