I have two cities with this problem.
Server: Asia
Region: Grand Korean Republic
City: Yeonan
Server: Asia
Region: Grand Korean Republic
City: KX Vegas
Both cities have space centers as the great work, and they both have cruise harbors. I believe I didn't have this problem until I plopped a cruise harbor. The main problem seems to be that they are getting too many tourists. "Current tourists" statistics under Gambling specialization are as follows:
Yeonan - 53,934 / 481,003
KX Vegas - 47,119 / 206,404
Most cities have tourists below 10,000.
The cities are slow to the point of being unplayable. There is no speed problem when I pause the game, But the game becomes increasingly slow as I speed up the game.
I'd like a fix for this issue, and if there is none, a reset for these cities. I've invested a lot of time for these cities, but if they're not salvageable, at least let me start again without restarting the whole region.