Yes breastfeeding can most definitely halt the process of your period. Especially breast feeding for such a long period of time. It is very common for a lot of women to not have a normal menstrual cycle until after they have weaned their child from breastfeeding. I know this was the case with myself as well.
Although absence of periods (amenorreah) is linked with breastfeeding, 15 months, whilst not impossible, seems rather an excessive length of time for this to continue. In Western countries, absence of periods for more than 6 months would be unusual, and more than a year very unusual. I would consult your doctor for other possible causes.
Nursing every 2 hours day and night will suppress ovulation. When ovulation is suppressed, periods will get delayed. Breastfeeding prevents periods only when nusrsing without supplementing. Its best natures form of birth control. It differs for each women, some women get their periods and some women may not get their periods regularly during breastfeeding.