ac15, does the ac15 have an effects loop?

Looking at Sweetwater.com, they have a photo of the back panel and from controls. It looks like on the far left of the back it has an effects in and out.

Even if it didn't, you could just run your guitar to the pedals, then out of the pedals into the Input on the front.

depends on how you define an ac15. I want to say that the custom classic that is really a 1/2 power ac30 custom classic ahs an effects loop. A vintage ac15 does not (its a 50s design and effects loops, even a basic power amp out and in setup, are a 70s idea), nor do either of the handwired series or the grey panel Marshall-made 90s reissues. Unless you play high-gain stuff with something like a mesa or soldano, effects loops (even tube buffered ones) are bad for your tone and offer very little in the way of benefits to your effects. A hi-Z preamp-in and poweramp-out can be handy as it switches out of the circuit when not in use. Ampeg was big on these in the 70s as was the notorious Alexander Dumble. If you like the vintage ac15 tone and want this primitive style of effects loops, Matchless style designs like the lightning, spitfire and nighthawk offer a bulletproof take on the ac15 platform with the added convenience of a preamp-out poweramp-in jack as an upcharge option (I think most well-known cloners like Nik at Ceriatone include them free).

Anything inserted in-line between the pre and power amp of a vox style circuit will inevitably hurt the dynamics and touch sensitivity, especially a proper ac15 with a small tube rectifier. The interaction of the entire circuit with your guitar is the sound of this type of amp, even used bone clean. Effects out front are one thing (though I recommend running with only a true bypass tuner for optimal awesomeness), but interrupting the flow of electrons from the pre to the power tubes is a bad idea if you are looking for the classic vox tone. The ac15 (like its cousin, the marshall 18 watt) is a total beast with a gradual transition from clean to dirty controlled by the player's hands and a wonderful singing sustain fueled by the tube rectifiers inherent sag. A proper ac15 with an ef86 preamp has a thick, nasty voice that really is its own effect and the lack of tone shaping means that 1 stage of preamplification has a big interaction with the phase splitter tube and the 2 power tubes. Don't mess with perfection. An ac30 top boost with an added effects loop isn't as blasphemous as the more complex circuit has a little less magic in the touch/sag department (though the ac30 is a great amp that offers lots of other unique benefits and I love the ones I have).

Hope I answered your question.

No, neither the Custom Classic as jimmarchi1 pointed out nor any other AC15 has an effects loop! Though the Top Boost tends to dig effects very well anyway. ;-)

Yeah, pretty much any effect that you might put in the loop of a more modern amp sounds great out front of a vox of any type. That includes studio rack effects. Example? The Edge and his Korg SDD3000 rack delays.