You have "PM" in your string without giving it a format code for it.
mysql> select STR_TO_DATE('10/29/2015 2:12 PM','%m/%d/%Y %h:%i') as d;
+---------------------+
| d |
+---------------------+
| 2015-10-29 02:12:00 |
+---------------------+
1 row in set, 1 warning (0.00 sec)
mysql> show warnings;
+---------+------+----------------------------------------------------------+
| Level | Code | Message |
+---------+------+----------------------------------------------------------+
| Warning | 1292 | Truncated incorrect datetime value: '10/29/2015 2:12 PM' |
+---------+------+----------------------------------------------------------+
Use %p
for the "AM"/"PM" part:
mysql> select STR_TO_DATE('10/29/2015 2:12 PM','%m/%d/%Y %h:%i %p');
+-------------------------------------------------------+
| STR_TO_DATE('10/29/2015 2:12 PM','%m/%d/%Y %h:%i %p') |
+-------------------------------------------------------+
| 2015-10-29 14:12:00 |
+-------------------------------------------------------+
1 row in set (0.00 sec)
(No warning when you do this.)