one object in 1k vertices is displayed well, while 100 objects with 10 vertices are frezzing

Why is one object with 100 thousand vertices in the scene displayed very vigorously, while 100 objects with 1 thousand vertices makes a heavy load on the processor ?
Here is the abstract example. In 1/60 sec I get the encoder. Then I have two options.
First
// Sphere
encoder.here is your buffer for the sphere
encoder.draw
// Cube
encoder.here is your buffer for the cube
encoder.draw
encoder.commit

Do I understand correct that the abstract code bellow(Second) will be more fast than code above(First)
Second
mesh = sphere + cube
encoder.here is your buffer for the mesh
encoder.draw
encoder.commit
?
one object in 1k vertices is displayed well, while 100 objects with 10 vertices are frezzing
 
 
Q