Will loading too many ACF Fields cause slow down?

This is hard to answer.

The (experienced) performance depends on how powerful your server is, how much simultaneous users are accessing your site etc.

With a dozen ACF-fields, you will most likely not experience any significant performance loss. A typical request to a WP page will often result in dozens of database queries, your 10 additional queries will hardly matter.

If you are worried about performance, you should look into caching the response completely. There are multiple plugins for that, or you could use servers like nginx or varnish that sit in front of your webserver and cache some responses.