Multiengine instrument commercial certificates as add-ons to single engine commercial certificates have no training minimum, per CFR 14 FAR 61.63. If you go in prepared for this training it is not impossible to take your checkride after 5 hours of dual instruction in an AMEL. I went for mine after 7, using the AllATPs add-on program. They have a 15 hour variation on it, and they may try and sell you 15 hours but obviously there is no requirement for it from the FAA, so try and go in prepared and insist you can do it in 10 hours or less wherever you do it.