Bless him. Like others have said work experience so often is an excruciating experience for all concerned. Especially in office based environments which of course so many jobs are these days. We get work experience kids in my work fairly frequently and while I do my best for them it's such a lot of effort to find things they can actually do and despite my best efforts they do end up bored and awkward or going home early a lot of the time (and the more anxious ones then get worked up and worried they're somehow making a bad impression or will get in trouble with their teachers for not doing whatever it is they imagined they were meant to be doing/achieving on their placement, they really really don't of course, the only ones I've ever had to actually complain about were actively rude/disrepectful or simply never showed up at all! everyone else gets glowing feedback even if they sat in the corner too scared to say anything all week!).
As someone else said in the 'olden days' you at least were able to give them some filing or photocopying or typing to do, or get them to do tea rounds or answer the phones, but none of that really happens in a modern office (or would require them getting set up with log ins and training on specific systems etc which really isn't practical for a 2 or 3 day work experience placement). Just being an observer sucks, even if you send them round different teams and people, all 'shadowing' involves is either sitting watching someone as they click and type on their computer, or attending meetings where they have no clue what's going on 
If it's an office type place he's in OP and he feels up to putting some suggestions forward for how he can use his time here are some things I get my work experience kids to do in my very, very boring corporate role (some of these are admittedly 'busy work' but it's good practice for the real world lol, and gives them something to take away and show for their week):
-Get some (non confidential) data (could be sales stats or workforce or financials/budgets, whatever's loosely relevant) and practice manipulating it in excel - making pivot tables, charts, graphs etc. He can teach himself to do this online if he doesn't know how.
-Summarize some (not too technical) articles from trade/professional journals or bulletins or even online webinars into headline bullet points for his supervisor to quickly read.
-Research a topic relevant to the workplace/department (could be a new technological development or a political change or a new business area or similar) - write this up into a briefing for a senior manager or stakeholder. Practice using PESTLE, SWOT and other analysis techniques to present the info. If relevant to the area then get them to write a staff newsletter/intranet item/communication or client briefing or social media post about the topic - get thinking about different audiences and how you present the same info in different formats (I can spin one single topic out into days on end of work for them lol)
-Using the same data or any other information, make a powerpoint slide deck explaining his findings and maybe even recommendations - if he's feeling really confident do a mini verbal presentation to his supervisor and/or some colleagues (although this is beyond many 15 year olds TBF)
-Practice taking minutes or action points for a meeting (non confidential/contentious obviously) which is a super useful workplace skill (I sometimes get them to do if from Teams recordings of a meeting rather than live as less pressure - if need be this can be 'helping' the actual minute taker rather than solo.