MODIS NDVI graph plot with R

Question

1. I have downloaded MODIS NDVI Aqua 16 days composite for the year 2015 and converted to tiff. There are 23 files.
2. I want to calculate the average of each raster and plot a graph where I have dates on x and NDVI values on the y axis.
3. I stacked them together and removed some part of the file names to make it short ( only for visual easyness) and stored in rasterNames
4. Next, I ran a loop to run through all the files, calculated mean and rescaled by 0.0001 to get the value in valid range (0-1)

Now, I got stock with what I have to do next to plot the graph where I have a vector avg_ndvi with values and rasterNames with the labels.

Is there any other smarter way to achieve the same? Because finally I am interested to add terra product in the same line and get 8 days composite but may show the labels only is some intervals , may be every month, or every 16 days.

#------------ Load the library--------
library(raster)
library(rgdal)
library(rasterVis)

setwd("C:/Working_Folder/R")
aqua_ndvi_path <- "aqua_ndvi_2015"
avg_ndvi<-vector()
date_ndvi <- vector()

#now load the Tiffs:
    all_ndvi <- list.files(aqua_ndvi_path,
                          full.names = TRUE,
                          pattern = ".tif$")
   ndvi_stack <- stack(all_ndvi) 
   # ndvi_stack_brick <- brick(ndvi_stack) 
   rasterNames  <- gsub("MYD13Q1_2015.","", names(ndvi_stack)) # remove some portion of file name
   rasterNames  <- gsub(".250m_16_days_NDVI","",rasterNames)   # remove some portion of the file name
   rasterNames  # This will give me short names so that i can use it as a label in graph/plot later


## --------- scale ndvi value by 10000 and calculate ndvi average of each raster and store it in the vector---------
   for (i in all_ndvi)     {
     j=cellStats(brick(i),mean)
     j=j*0.0001
     avg_ndvi<- c(avg_ndvi,j)
      }
   print(avg_ndvi)