Big table with simple queries, but with a lot of text, is it bad for performance? I am making cache table for website. It will have no problem with indexes (one unique index, simple quires), but it will have a lot of utf text. It will be 10-15gb (2 mln rows).
Caching will help a lot for saving cpu usage, without cache every page has many complex queries.

Is it ok two have such a big table? It will be queried only with "SELECT text WHERE id = $id" several times a second.
MySQL itself can handle primary key selects very efficiently. However cached content does not require transactional engine so it would be much faster to store this kind of data in various key-value storages. Memcached is the first one to consider.