I run hot, so prefer to carry all my load on the bike rather than sweating with a rucksack; for 15 miles doubly so. If you have rack eyes then a single pannier should take all that with no problems; if not, then this kind of load is exactly what Carradice saddlebags were designed for and have been carrying for 80-odd years. If you might need to bring a uniform back I'd go for one of the larger ones: maybe a Pendle or Nelson.
I run hot, so prefer to carry all my load on the bike rather than sweating with a rucksack; for 15 miles doubly so. If you have rack eyes then a single pannier should take all that with no problems; if not, then this kind of load is exactly what Carradice saddlebags were designed for and have been carrying for 80-odd years. If you might need to bring a uniform back I'd go for one of the larger ones: maybe a Pendle or Nelson.