Question
Rpi3V Stretch and Waveshare GSM/GPRS/GNSS HAT for GPS an Internet.
Used USB-UART and Python 3 location OK
SIM868_PPP_Dail-up_Networking ttyUSB0 connection very slow
Not able to do 3G connection though I update with APN of the service
provider.
Answer
Well, the user guide already explained why Rpi is slow. They fiddled something but using 115k baud AT command to do PPPoE is of course slow. The service provider might also set lower priority to poor 2G customers
Your board is only 2G GSM/GPRS. So you can not do 3G. Bad luck! :(


Update 2019may17hkt1121
One suggestion is to use something like Hologram Nova USB Modem. See references below for more details.
References
Raspberry Pi : How to access the Internet using GSM / GPRS Modem (SIM900/SIM800)
GSM/GPRS TTL UART MODEM-SIM900 - Rhydolabz
Point-to-Point Protocol over Ethernet (PPPoE) - Wikipedia
List of mobile phone generations
2G/3G/4G Hologram Nova USB Modem Datasheet
Hologram Nova is ... open source cellular USB modem, ... with AT
command interface.
Global IoT SIM Card
SIM card for global IoT applications, covering over 196 countries,
550+ carriers, with flexible pricing: pay-as-you-go rates or monthly
plans
WaveShare 4G/3G/2G/GSM/GPRS/GNSS (LTE CAT4, for China) HAT for Raspberry Pi US$$66
WaveShare GSM/GPRS/GNSS/Bluetooth HAT for Raspberry Pi US$34
WaveShare GSM/GPRS/GNSS HAT, Compatible with Raspberry Pi 2B/3B/Zeo/Zero W
WaveShare L76X GPS HAT
WaveShare GSM/GPRS/GPS HAT User Manual
Simple script to use Waveshare GSM/GPRS/GNSS/Bluetooth HAT for Raspberry Pi hat GPS functions
Waveshare GSM/Bluetooth Hat Forum Discussion
Waveshare GSM/GPRS/GNSS HAT not connecting to Cellular network
WaveShare SIM868 GSM GPRS GNSS Bluetooth HAT for Rpi 2B/3B/Zero/Zero W support
Raspberry Pi GSM Module – Mobile Internet (LTE, 3G, UMTS)
The Raspberry Pi can be connected to the Internet very quickly and
easily via the local network. But what if you also need a mobile
Internet connection outside your own WLAN? There are GSM modules /
Surfsticks (mostly from Huawei), which can be connected via USB.
Sometimes are such GSM modules, which support 3G, UMTS and sometimes
even LTE, given free with a mobile phone contract which includes an
Internet option.
This tutorial shows how to connect Raspberry Pi to the internet using
GSM modules.
- End of Answer -
Is there any option to obtain the internet from such a module except using wifi? I mean to run RPI with the internet as a separate device. I searched for different modules and bought this one but now as explained it is not working with the speed I want :( Any suggestion about an alternative option, please?
Thanks again!
– Sachz May 14 '19 at 16:49