Playing SH3 again with Windows 10 Pro 64 bit

[Yattky]

Dear members

Good day

I'm playing SH3 with Windows 10 pro 64bit again and enjoy it but I have a problem while doing it.
The game in motion gets gradually slower and slower.
At the beginning, the frame rate is 20-30
but at the end, it is down to under 10.
(Especially when I meet enemies, the rate is rapidly decreased and never recovered.)
I think my pc spec is improved more than the one in 2005 SH3 was released, but there can be some setting incorrectly (especially in my graphic card).
However I would like to ask you the way of fix by return.
For your reference, my pc spec is as follows:

CPU: Intel core i7-4790K CPU@4.00GHZ
RAM: DDR3 12.0GB
MOTHER BOARD: ASUS H97-PRO
OS:WINDOWS 10 PRO 64BIT
HARD DISC:SEAGATE SSHD ST4000DX 4TB (My SH3 installed in D drive.)
GRAPHIC BOARD: GEFORCE GTX970

Should I renew my pc?
I installed also 4GB patch in it, so please advise me if it affects the problem.
Looking forward to your reply.

B.Rgds
Yattky