Odd observation here, you have a load of time being spent in AutoCompleteGetKeywords(), which should be nearly instant. Have you heavily modified your color coding settings? I guess it could get laggy if your settings introduce thousands of new keywords, otherwise I do not have a very good explanation for why it is spending a lot of time there. That function was heavily optimized for SlickEdit 2021 (v26).
From your description, it appears that you are getting ahead of Auto-Complete, but if it's getting in your way, then what is *actually* happening is that it is getting ahead of you. I would recommend increasing the following settings:
Tools > Options... > Editing > Context Tagging > Auto-Complete performance tuning
Display Auto-Complete after (ms) idle: (Default 250ms, increase it to a full half-second or more)
Update Auto-Complete after (ms) idle: (Default 50ms, increase it to 250ms)
The first setting adjusts when Auto-Complete will kick in and show options, the second adjust how quickly Auto-Complete will recalculate things after you type more characters to further narrow the result. Increasing both gives you more time to type unimpeded.
The same dialog has "Symbol Coloring performance tuning", which is somewhat the same story. Increase the following setting to keep Symbol Coloring at bay when you are busy typing.
Update Symbol Coloring after (ms) idle: Default 500, make it a full second or more
Also, you can decrease the scope of Symbol Coloring's work by changing this setting:
Windows to color: Change it to "Current Window" to make minimize the amount of work Symbol Coloring has to do.
Another tweak to Symbol Coloring performance that may be relevant for you is Document > C/C++ Options... > Appearance > Symbol Coloring > Override color for Library and User Defined keywords (turn it off). If you have modified your C/C++ Lexer with a ton of new Library or User Defined keywords, you can let Symbol Coloring take the day off when it sees those and trust the colors you have already configured.