45 minutes would only work for flights involving CX and KA, and even then it would be tight. Since CX/KA doesn't fly to Ko Samui then the answer is definitely No.

Whether you can check bags through depends on the interlining arrangements of the airlines concerned. T1 and T2 are simply different landside check-in areas, not separate terminals; if you are doing an airside transit then they are irrelevant - all gates are in the same terminal, although some are bus gates.