There is a mention of the "Me-115" in FM 30-35 "Military Intelligence - Identification of German Aircraft - March 11, 1942", from the US War Department.
No images or details other than an armament of two cannon and two mgs, 400 mph top speed, and one 2000 hp DB605. The last item makes me wonder if "Me-115" was an assumed new designation for the upcoming Bf-109G?
Presumably the engine on the Flight "Me-115" is based on descriptions of the DB604 but that X-24 engine is bigger and more powerful than the 2000 hp listed in FM 30-35. Perhaps at the time there was confusion between the DB604 and DB605?
BTW, FM 30-35 does list the Heinkel He-115 as well.
Apologies for bumping this old thread, but I just had a look at the original flight global article and the so called 'X-engine' appears to be a confusion between the Rolls-Royce Vulture and the DB-606 both of which are mentioned in the article. As I remember correctly the only Hawker Typhoon fitted with a Vulture was one of the few aircraft to not have problems with that powerplant.
If there is any basis in truth to that Flight report, the X-24 engine in question was more likely the DB 604. Smaller than the DB 606, the DB 604 was also intended as a bomber powerplant -- not for fighters.
The DB 604 was abandoned in Sept 1942, some months after Me 155 development began. It's a long shot, but is it possible that "Me 115" was a garbling of the Me 155 designation?
BTW, the Vulture-powerd Typhoon analogue was the Hawker Tornado.