It’s not too bad. We’re sort of a shoe-string organization, and are using the non-profit free account. If the performance turns out not to be acceptable when more folks are using it (we have a staff of maybe 20 who might use it), I’ll try to persuade the board to upgrade the account.
Evidently this is a not-uncommon problem with ownCloud. Rather than bother fixing it, I just downloaded the two apps I wanted to my personal Linux box, gunzipped and untarred them, then SFTPed the resulting directory structures onto the ownCloud instance in the apps directory, where the installer would have put them anyway. The gallery app is working as expected; the Onlyoffice app is enabled, but I haven’t set up a document server for it yet (waiting to see if the board even cares about collaborative document editing).