Oxwall software itself isn't slow to run. Once you start adding more and more plugins though, it has the possibility of running slower - but the original core and original plugins do not.
I will add, one of the main issues that it could be running slow for you is because of your hosting provider and/or package you currently have with them. Some hosting providers limit their users to a certain amount of resources - this is especially the case if you are on a "shared" hosting plan. Your best bet would be to upgrade your server and add additional resources as needed to keep your oxwall site running smoothly.
As your community grows, so will the content build-up on your server - so easily said, once you see a large flux in members and member usage on your site, add additional resources to keep your site running smoothly. This is the case for any, if not all, social network websites.
Just my two cents. I've never had an issue with performance from oxwall - sure some plugins tend to not work as they say it should, but for the most part, the devs fix it fairly quick. And if not, just be patient - some plugin developers have a ton of different plugins on here and they have a period where they try to improve each plugin one-by-one in a specific order they may have...All in all, most get updated quick once a new version of the core software comes out, and for those that don't - well....be careful. It may mean that dev no longer is working on it.