My Dell Inspiron 15 3521 laptop runs super slow after I upgraded to 16GB of Ram. Why? It's a Celeron 100 7U 1.5GHZ.?

Update: Is it the processor? The ram sticks match and the computer recognizes them. No virus or malware issues. Do I need an SSD drive?
Update 2: Would the laptop operate faster downgrading to 8GB?
6 answers 6