The el-Niño of 2015 had all the characteristics of being just as powerful as the el-Niño of 1997 and 1998. There is however a few small differences. The el-Niño of 1998 occurred 2 years before solar max, in other words there was still high solar climate forcing in 1998, 2000 and 2001.
The 2015 el-Niño is occurring just after solar max, in other words there will be less solar forcing in 2016, 2017 and 2018. The el-Niño of 1998 started in 1997 and ended in 1998; the current el-Niño started in early 2015 and will most likely end in June 2016 and followed by a powerful La-Nina.
The current el-Niño also has additional support from above normal ocean temperature stretching from the equator all the way up to Alaska which translates into massive amounts of additional water vapour which is a greenhouse gas.
The strong el-Niño of 1998 was followed by a relative large drop in temperature in 2000 and 2001, most probably due to the high volume of cloud formation due to water vapour which reflexed the sun light.
In conclusion we can expect the same to happen in 2017 and 2018 with two exceptions low solar forcing and more cosmic rays translating into a much bigger drop in temperature.