Sequentially coupled thermal stress analysis in ABAQUS

Dear all, 
 

 I'm a master degree student. I am modeling a composite slab subjected to standard fire (ISO 834-1). I have two models, a heat transfer model in ABAQUS / standard and a mechanical model in ABAQUS / Explicit due to convergences issues in concrete damage plasticity.
 
 In my heat transfer model, I apply heat for 6000 seconds according to my experimental program.
 
 In my mechanical model I firstly apply the load and in the second step I import the nodal temperatures as a function of time as a predefined field. The problem is the computational costs in this second step that greatly increase my analysis time.
 
 I would like to know how can I accelerate the development of temperatures in my mechanical model?
 
 Thanks in advance.