The Sukhoi Su-15 was developed primarily because of the Soviet Unions great need for a capable high-speed high-altitude interceptor in the 1950's. The Sukhoi design bureu was tasked with the construction of the swept-wing S-1 tactical fighter and the delta-winged T-3 interceptor.
The Su-1 'Fitter' which first flew in 1955 later developed into the Su-7 which in turn developed into the very successful Su-17,20,22 variable wing geometry attack aircrafts. The T-3 on the other hand developed into the Su-7 'Fishpot'. Unfortunately the Su-9 lacked performance in both operational as well as radar range. This led to the development of the Su-15 'Flagon', not counting the half-failure of Su-11 (a bigger version of the Su-9). The Su-15 after lots of prototypes first flew operationally in 1965. During it's operational time it guarded the Soviet Unions borders right up until the desintegration of the USSR.
The first version of the Su-15 had compared to earlier versions of Soviet supersonic interceptors both long-range and a powerful radar. Despite high landing speed due to it's heavy weight and small delta winds it was very much liked by it's pilots given it's otherwise good handling in the air. It was armed with two R-98 missiles (AA-3 ANAB) which were available both in IR and Radar-guided versions. A much prized advantage of the Su-15 compared to earlier aircrafts was its increased ability to engage targets flying at low and medium altitude and also from the head-on position.
Production of the T-model began in 1971 and that later became TM with the modernised Taifun-M radar. The Su-15 had at this point evolved with extended double-delta wings to lower the high approroach speed and a spherical nosecone replaced the conical cone to make room for the bigger radar. Some say the spherical cone was added to improve aerodynamics but in truth it added more drag. The TM also had smaller inner weapon pylons under the wings to carry R-60 (AA-8 APHID) missiles, this was done to satisfy the need of a dogfighting capability. The Soviet command also wanted to make the Su-15 available as a fighter bomber should the need arise and so the fuselage hardpoints were upgraded to carry gunpods, bombs and heavy attack rockets. The outer wing pylons were also modified to carry rockets pods.
During operational neither of these attack weapons were ever used and although the weapons could be used no truly efficient fire-control were ever added. The gunpods were used but only to increase the aircrafts dogfight capabilities however the simple collimator sight didn't make this an easy task.