The birth figures from the Central Statistics Office show that 1,187 teenagers had babies last year, but the number of such births has declined over the past 15 years.
The HSE Sexual Health and Crisis Pregnancy Programme pointed out that births to teenagers had fallen by 62% since 2001 when there were 3,087.
The health authority said the 2015 figures showed a further decrease of 66 births to teenagers, compared to 2014 when there were 1,253.
The HSE said the relationship and sexuality eduction programme in schools and youth centres was contributing to the decline.
It also pointed out that there had been a decline of 72% in the number of teenagers giving Irish addresses at abortion clinics in Britain since 2001.
Just over half (53%) of births outside marriage or civil partnership last year were to mothers under 30. The average age of first-time mothers last year was 30.7 years, up 0.2 years from 2014.
The CSO figures show 65,909 births were registered last year, a decrease of 1,553 on 2014. However, the 2015 figure is 8% higher than in 2005 where there were 61,042 births.
However, the total fertility rate for Ireland has fallen in the past two years from 1.95 to 1.94. A value of 2.1 is considered to be the level at which the population would replace itself, in the long run, ignoring migration.
More than three-quarters of the births were to Irish mothers, with just over 6% to mothers from non-EU countries. Almost 40% of the births (24,867) were to first-time mothers while 35% (23,0360) were to second-time mothers. There were 224 children born to mothers who were aged 45 and over.
Over a third (36%) of births last year were outside marriage, with almost 60% to cohabiting parents.
There were 205 infant deaths registered last year —an infant mortality rate of 3.1 deaths per 1,000 live births, a decrease of 0.6 from 2014.
Ten years earlier in 2005 there were 244 infant deaths registered which equated to an infant mortality rate of 4 per 1,000 live births.
There were 151 neonatal deaths (babies aged under four weeks) registered last year — a death rate of 2.3 per 1,000 live births and a decrease of 0.4 from 2014.
There were 22,116 marriages registered last year of which 91 were same-sex marriages. However, the marriage rate in 2015 was 4.8 per 1,000 of the population, the same rate as in 2014.
The number of deaths registered at 29,952 for 2015 is almost 10% higher than in 2005 when there were 27,441.
Deaths last year were caused by diseases of the circulatory system (31%), cancer (30%), and respiratory disease (13%). About 5% of all deaths (1,439) were due to accidents, suicide and other external causes.
There were 451 suicides registered last year compared with 459 in 2014. Men accounted for 83% of all recorded suicide deaths in 2015.
The natural increase (births minus deaths) last year was 35,957 — almost 6.3% lower than the natural increase of 38,367 in 2014.