OK, it’s Autumn, not Spring, but you know what I mean. Any time is a good time to ask yourself: is there stuff on my website that nobody would miss? Because if there is, there’s also a good SEO-related argument for getting rid of it.
For a start, your site has what’s called ‘link equity’ in Google, a value given by the external links pointing to it. This link equity flows through the site, and is diluted across all the pages. Get rid of a page, and that’s more available to the rest. In addition, search engines will only allocate your site a certain amount of crawling resource, and the more pages you have, the less often they’ll get examined.
So what can go? That exhibition preview from 2015. An old press release introducing a product line which is now just a legacy product. That much will be obvious. But also take a look at Google Analytics over the longest period possible, and compare it to the last 6 months. What pages are no longer being viewed? Use Search Console to see if they’ve appeared in the search results at all. If not, they can be deleted – probably without even a redirection – and nobody will care. If there’s some activity, or you’re in any doubt, set up a 301 redirect to a suitable alternative page.
You might also look at the time that users spend on a page. If it’s consistently low, is it because the page has very little value? Can it be improved, or amalgamated with another page? Indeed, amalgamating old pages to form a single, more substantial article can have obvious benefits for users and search engines alike.
I have seen anecdotes of sites removing half or more of their content, stretching back many years, and seeing a substantial SEO benefit from doing so. It’s worth investigating.