15 day visa exemption limit

As a Singapore passport holder, there is a 15 day visa exemption. If my stay is exactly 15 days (including arrival day and departure day), will there be a problem? I wish to stay in mainland China for 15 days, visit Taiwan for a few weeks, then go back to mainland China for another 15 days, will each visit be considered a separate entry? Will I need to get a Visa in this case?