Did you get any error messages when installing?
Did you add the files and enable the extension after using PECL?
To my knowledge Ubuntu 16.04 uses php7, support for php7 doesn’t start in phpredis until v3.0.0 and the debian repositories version of php-redis is v2.2.5 (last time I checked), so whilst it might appear to work using v2.2.5 with php7, it might not be 100%.
For the record, I’ve just checked a Debian Stretch on amd64 instance running php7 with the redis extension installed via PECL and that has the file you appear to be missing
pb66@test2:~$ ls -la /usr/lib/php/20151012/redis.so
-rw-r--r-- 1 root root 1809640 Jan 17 09:34 /usr/lib/php/20151012/redis.so
(see the Php-Redis 3.1.1? discussion for some insight to the versions, package managers and install methods).