It takes about 750ms to open on my computer, which I think is too long. Unfortunately, I cannot see a way to speed it up. The Options dialog has a huge number of settings/controls. The only solution would be to move some option groups to their own separate dialogs.
If you install mIRC using the "portable" option in the installer into a clean, empty folder and test that, on the same Windows 10 installation as your current mIRC, do you see the same issue?
