Stick with boring new job vs. old job opening?

Left an old job which I’d had for over a decade 18 months ago to start my own business (long itch I had to scratch, which didn’t work out). Really regretted quitting my job afterwards, but finally found a new job, in a similar vein, which has decent pay and T&C.
However, 5 weeks in, it is boring and frustrating as hell.
I'm a creative kind, but I've no creative outlet (or opinion) whatsoever in this new job. Whereas I did in my previous career, before leaving to try my own thing. Without sounding conceited, people still tell me that I was doing a great job there and the place is really lacking without me.
I’ve now learned that, a few weeks ago, my old boss – who I’m still on good terms with – was on the verge of asking me to go back in a new (creative, all-encompassing) role before I got my current job.
The old workplace is unorthodox… it was crazy at times. The new place is clinical. Everything is where it should be in terms of management, HR, etc. But there are so many systems and procedures (and layers of bossmania) it’s counter-productive. And what I’m doing in terms of subject matter is mind-numbing.
Just wondering should I contact my old boss for a chat (it’s informal like that) or should I give the new job more time? Just don’t want to get into it too deep if it’s something I’m not going to be happy in or committed to.