Hello @Nikoloz
Thanks for using Microsoft Q&A platform. There is no public SLA for Bing Spell Check API for now, I will forward this feedback to product group so that customer has a better understand of the response time.
The time the API returns the output contains two parts - the latency and the response time
The latency may be effected by your internet, location, ...
The response time is effected by the length of your query, target language,..
Based my personal experience, the time may take 200ms to 500ms typically, sometimes it will become longer but that is not the basic case. Please let me know if 2000ms become the basical case, I am willing to help you connect with support team to check on the backlog.
I hope this helps. Please let me know if you need further help.
Regards,
Yutong
-Please kindly accept the answer if you feel helpful to support the community, thanks a lot.