Have you ever heard about the package dbplyr
(with the b)?
I would recommend it because this package enables your dplyr
(with no b) to be used with SQL databases.
There are many advantages since the way you interact with your databases will shift
from this:

to this:

These images are extracted from a great article entitled "Databases using R" by Edgar Ruiz (2017). You should take a look at it HERE for more details.
The main advantages presented by Mr. Ruiz are, and I quote:
"
1) Run data exploration over all of the data - Instead of coming up with a plan to decide what data to import, we can focus on analyzing the data inside the database, which in turn should yield faster insights.
2) Use the SQL Engine to run the data transformations - We are, in effect, pushing the computation to the database because dplyr is sending SQL queries to the database.
3) Collect a targeted dataset - After become familiar with the data and choosing the data points that will either be shared or modeled, a final query can then be used to bring back only that data into memory in R.
4) All your code is in R! - Because we are using dplyr to communicate with the database, there is no need to change language, or tools, to perform the data exploration. "
So, you will probably gain the speed you are looking for with dbplyr
/dplyr
.
You should give it a try.
You can find more information about it and how to establish the connection with your PostgreSQL Server using the DBI package at:
https://cran.r-project.org/web/packages/dbplyr/vignettes/dbplyr.html
and
https://rviews.rstudio.com/2017/05/17/databases-using-r/